Scanning Electron Microscopy (SEM)

A standard scanning electron microscope (SEM) is typically used for low-to-medium magnification (10-50,000×) imaging of conductive samples. For non-conductive samples, a conductive coating of carbon, gold, chromium, etc. must be applied to avoid charging effects. A variable-pressure SEM (low vacuum or environmental) is used for non-conductive specimens like glass, polymers/paint and biological materials without applying a conductive coating to the specimen. Higher magnification (100,000-1,000,000×) requires the use of a field emission scanning electron microscope (FESEM).

In the SEM, samples are illuminated with a focused beam of electrons in a vacuum chamber. These electrons interact with the sample in numerous ways, creating various radiation types including the production of secondary electrons, backscattered electrons and characteristic x-rays. These signals are used for imaging and compositional analysis at high spatial resolution. Compared to light microscopy, SEM offers higher resolution (as good as 3.0 nm), greater depth of field, longer working distances and better surface sensitivity. Images of backscattered electrons (BE) provide compositional information, since the BE signal intensity of a material is proportional to its average atomic number. X-rays generated by the electron beam are detected and analyzed with an energy dispersive x-ray spectrometer (EDS). EDS spectra can be used to obtain a qualitative and quantitative elemental analysis at micrometer spatial resolution. FESEM offers resolution as good as 0.6 nm.

Instrumentation

McCrone Associates uses several scanning electron microscopes:

JSM-IT500HR InTouchscope

This new high-brightness, long-life emitter delivers exceptional fidelity field emission imaging capability at any kV. The microscope also includes a large specimen chamber with variable pressure capabilities. One of the most exciting new capabilities is the Zeromag feature that incorporates digital color camera imaging with the electron column imaging to seamlessly navigate large samples. Color images of your sample automatically transition with increases in the magnification from the zero magnification color optical image to the electron imaging mode. The microscope also contains a new integrated JEOL energy dispersive x-ray spectrometer and an added Oxford Instruments energy dispersive x-ray spectrometer for exceptional analytical capability.

JEOL JSM-6610LV low vacuum SEM

This system offers improved resolution in low vacuum mode and a new enhanced backscattered electron detector for improved resolution under all vacuum conditions. The system is equipped with an AZtec and INCA microanalysis system with 80 mm2 with silicon drift detector from Oxford Instruments. Operation in low vacuum (LV) mode permits examination and x-ray microanalysis of non-conductive samples without coating. The computer-controlled stage and digital imaging system allow automated particle and feature analysis and unattended x-ray mapping.

JEOL JSM-7500F FESEM

Ultrahigh resolution imaging is possible with magnifications up to 1,000,000×. A wide range of operating modes and detectors are optimized for surface imaging of materials at the nanometer scale. The FESEM is equipped with a ThermoFisher Scientific System Six microanalysis system with 10 mm2 silicon drift detector.

JEOL JSM-7600F FESEM

Ultrahigh resolution imaging is possible with magnifications up to 1,000,000×. A wide range of operating modes and detectors are optimized for surface imaging of materials at the nanometer scale. The FESEM is equipped with an AZtec and INCA microanalysis system with 50 mm2 silicon drift detector, as well as INCAWave wavelength dispersive spectrometer (WDS) system from Oxford Instruments. The wide range of operating modes and detectors are optimized for surface imaging and analysis of materials at the nanometer scale. The WDS system helps in instances of spectral overlaps in EDS and also permits measurement of elements to lower concentrations than EDS.